Global contribution of echinoderms to the marine carbon cycle: CaCO₃ budget and benthic compartments

Abstract

Abstract. The contribution of carbonate-producing benthic organisms to the global marine carbon budget has been overlooked, the prevailing view being that calcium carbonate (CaCO 3 ) is predominantly produced and exported by marine plankton in the ''biological pump.'' Here, we provide the first estimation of the global contribution of echinoderms to the marine inorganic and organic carbon cycle, based on organism-level measurements from species of the five echinoderm classes. Echinoderms' global CaCO 3 contribution amounts to ;0.861 Pg CaCO 3 /yr (0.102 Pg C/yr of inorganic carbon) as a production rate, and ;2.11 Pg CaCO 3 (0.25 Pg C of inorganic carbon) as a standing stock from the shelves, slopes, and abyssal depths. Echinoderm inorganic carbon production (0.102 Pg C/yr) is less than the global pelagic production (0.4-1.8 Pg C/yr) and similar to the estimates for carbonate shelves globally (0.024-0.120 Pg C/yr Áyr À1 as inorganic carbon) for the slope on a global scale. The biogeography of the CaCO 3 standing stocks of echinoderms showed strong latitudinal variability. More than 80% of the global CaCO 3 production from echinoderms occurs between 0 and 800 m, with the highest contribution attributed to the shelf and upper slope. We provide a global distribution of echinoderm populations in the context of global calcite saturation horizons, since undersaturated waters with respect to mineral phases are surfacing. This shallowing is a direct consequence of ocean acidification, and in some places it may reach the shelf and upper slope permanently, where the highest CaCO 3 standing stocks from echinoderms originate. These organism-level data contribute substantially to the assessment of global carbonate inventories, which at present are poorly estimated. Additionally, it is desirable to include these benthic compartments in coupled global biogeochemical models representing the ''biological pump'' and its feedbacks, since at present all efforts have focused on pelagic processes, dominated by coccolithophores. The omission of the benthic processes from modeling will only diminish the understanding of elemental fluxes at large scales and any future prediction of climate change scenarios.

δ13C and δ18O signatures from sea urchin skeleton: importance of diet type in metabolic contributions

“…On the other hand, because a large fraction of echinoderm carbon may come from their diet, this would imply that a significant amount (e.g. 30 to 40%) of their global annual inorganic carbon production of 0.102 Pg yr −1 (Lebrato et al 2010) is not being removed directly from seawater and must be accounted for in their contributions to the functioning of biogeochemical cycles (Lebrato et al 2010).…”

“…derms have a standing stock of ~0.25 Pg and global production rates (0.102 Pg C yr −1 ; Lebrato et al 2010) that are similar to coral reefs (0.108 Pg C yr −1 ; Iglesias- Rodriguez et al 2002) and exceed that of other benthic producers such as Halimeda bioherms (0.048 Pg C yr −1…”

“…Aside from their role in the biogeochemical cycle of marine carbonates (Dupont et al 2010, Lebrato et al 2010, sea urchins also play major ecological roles in the control of macrophyte communities and in the transfer of biomass and energy to higher trophic levels (e.g. Heck & Valentine 1995, Shears & Babcock 2003, Prado et al 2007).…”

Sea urchin response to rising pCO2 shows ocean acidification may fundamentally alter the chemistry of marine skeletons

“…Here we studied the effects of increased pCO 2 on sea urchins, which are important for three main reasons. Firstly, they are often keystone species in shallow rocky shore ecosystems since their grazing can structure communities affecting commercially important crustaceans and fish (Sala et al, 1998); secondly, they contribute an estimated 66.7 g CaCO 3 m -2 y -1 to annual oceanic CaCO 3 production, thus influencing global bio-geochemical cycles (Lebrato et al, 2010); and thirdly, they support a fishing industry worth approximately 89 million US dollars (FAOSTAT, 2013).…”

Links between deep‐sea respiration and community dynamics

“…Benthic echinoderms have been estimated to contribute to a substantial portion of inorganic C 388 production globally (up to about 1/4 that of pelagic inorganic C production, Lebrato et al 2010). …”